The invention concerns a multilayer headbox of a paper machine with a slice nozzle subdivided by lamellae of flexible installation, in which slice nozzle there is for each stock suspension an aperture space provided which extends across the machine width. Furthermore, the invention concerns a method for adjusting the relative velocities of the individual stock suspensions at the nozzle exit.
A headbox of that type is known, e.g., from DE-OS 37 04 462. Its aperture spaces being supplied independently from one another with stock suspensions, said headbox serves the manufacture of multilayer paper webs. To adjust different velocities and pressures of the stock suspension in the individual spaces, the lamellae between individual aperture spaces are pivotable about their longitudinal axis and are manually adjusted from outside. Disadvantageous is here that, when the quantity passing through the headbox changes, the interrelationship of stock suspension velocities between individual layers changes, requiring readaptation by manual adjustment. A further disadvantage is that the necessary accuracy of adjustment cannot be achieved at all or only at extraordinary expense.
Moreover, reference is made to patent document DE 31 01 407 A1. This document depicts a multilayer headbox whose built-in lamellae are installed flexibly. The lamellae shown there, however, aim to maximally equalize the flow velocities of the different layers.
Hence, it is also known to fashion the lamellae in the aperture space flexible across their entire length, allowing them to automatically adjust in such a way that equal pressure prevails at any point in all aperture spaces. A flow adjustment in the individual nozzle spaces and a mutually independent adjustment of the exit gaps for the individual paper layers, however, is not possible thereby.
For some time now it has been desired to influence the velocities of the individual jets of a multilayer headbox in such a way that the differential velocities between individual jets will change. In the cited prior art this is carried out by manual adjustment of the individual lamellae. It shows here, however, that it is very difficult to adjust the lamellae, which are up to 10 meters long, to the necessary accuracy of a few hundredths of a millimeter against the forces of flow in a fashion which is constant across the machine width. Furthermore, altering the conditions of throughput leads to different velocity ratios between individual layers, whereby readjustment becomes necessary.